Multilayer thick film circuits are typically fabricated by screen printing layers or patterns of dielectric and conductive materials onto a ceramic substrate and firing at elevated temperature to fuse the dielectric and conductive materials to the substrate. In most cases it is necessary to sequentially print, fire and cool each layer before the next layer can be applied. The firing process can involve temperatures as high as 1000.degree. C. which can lead to severe warpage of the substrate during the subsequent cooling stage.
U.S. Pat. No. 4,655,864 discloses a dielectric composition comprising a dispersion of finely divided solids comprising: (a) 40-70% volume noncrystallizable glass, (b) 60-30% vol. of a mixture of refractory oxides, (c) polymeric binder and (d) volatile organic solvent. The glass disclosed in the '864 patent is a single glass having a softening point of at least 500.degree. C. and a viscosity of 1.times.10.sup.6 poises or less at 825.degree.-1025.degree. C. The mixture of refractory oxides consists of A1.sub.2 O.sub.3 as the primary refractory and a secondary refractory such as quartz, CaZrO.sub.3 or fused silica.
U.S. Pat. No. 4,654,095 discloses a dielectric composition comprising an admixture of finely divided solids comprising:
(a) 50-17% wt. noncrystallizable glass having a deformation temp (T.sub.d) of 580.degree.-625.degree. C., a softening point (T.sub.s) of 630.degree.-700.degree. C., and (T.sub.s -T.sub.d) is 50.degree.-75.degree. C., and; PA1 (b) 50-25% wt. refractory which is substantially insoluble in the glass at 825.degree.-900.degree. C.
The present invention is an improvement over the prior art dielectric compositions in that this invention utilizes a blend or admixture of glasses to tailor the CTE of the glass blend to match that of the substrate. This gives great flexibility in preparing glass blends having a wide range of CTE values and results in significantly reduced warpage of the substrate.